Ganbare Goemon 2, with it's Castlevania level and easter eggs. I never played any of the games in this series when they were new, however I watched Korone and Okayu get to the Akumajou level in 2 and fight Dracula, I remember being shocked and genuinely interested in the franchise for the first time. Sadly the only GG game I own physically is the Famicom Mini version on GBA.